Systemic lupus erthematosus is an autoimmune disease of unknown etiology. There is convincing epidemiological evidence that SLE clusters in families, suggesting a genetic basis for the disease. Our hypothesis, based on a large body of evidence, is that SLE is an oligogenic disease, with the inheritance of a few genes other than MHC and TCR contributing to susceptibility. We propose to use gene mapping with highly informative, short tandem repeat polymorphism's (STRPs) in sibling pairs and multiplex families with SLE. In the course of the study we will establish a detailed database of clinical and family history data, determine Class II genotypes, and establish a repository of sera, DNA and immortalized cell lines for each subject.